1. Field of the Invention
The invention relates to a power supply system and a vehicle equipped with the power supply system and, more particularly, to charging control for charging an electrical storage device equipped for a vehicle with electric power supplied from an external power supply.
2. Description of the Related Art
In recent years, as an environmentally friendly vehicle, an electromotive vehicle that is equipped with an electrical storage device (for example, a secondary battery, a capacitor, or the like) and that is propelled by driving force generated from electric power stored in the electrical storage device receives attention. The electromotive vehicle, for example, includes an electric vehicle, a hybrid vehicle, a fuel cell vehicle, and the like. Then, there is proposed a technique for charging electrical storage devices equipped for these electromotive vehicles by a commercial power supply having a high power generation efficiency.
There is known a hybrid vehicle that is able to charge an in-vehicle electrical storage device from a power supply (hereinafter, also simply referred to as “external power supply”) outside the vehicle (hereinafter, also simply referred to as “external charging”) as in the case of an electric vehicle. For example, there is known a so-called plug-in hybrid vehicle that is able to charge an electrical storage device using a power supply of an ordinary household in such a manner that a power supply wall outlet installed in a house is connected to a charging inlet provided for a vehicle via a charging cable. By so doing, it may be expected to improve the fuel consumption efficiency of the hybrid vehicle.
Japanese Patent Application Publication No. 2009-027774 (JP-A-2009-027774) describes a technique for, in a vehicle equipped with a battery that allows external charging, continuously operating a DC/DC converter, which is used to step down the voltage of the battery to drive auxiliary loads and charge an auxiliary battery, during operation of the vehicle and intermittently operating the DC/DC converter during external charging.
With the technique described in JP-A-2009-027774, in comparison with a case where the DC/DC converter is constantly driven during external charging, a loss at the time of power conversion carried out by the DC/DC converter may be reduced through intermittent operation, so it is possible to improve the charging efficiency.
Such a DC/DC converter not only charges the auxiliary battery but also drives all the auxiliary loads of the vehicle during operation of the vehicle, so a relatively high-power DC/DC converter is employed.
However, during external charging, a smaller number of auxiliary loads are driven as compared with that during operation of the vehicle, so driving the DC/DC converter may exhibit excessive performance. In such a case, the power conversion efficiency of the DC/DC converter becomes poor because of low-power power conversion.